The present invention relates in general to a protective shield for chemical vapor deposition systems and, more particularly, to a gas shield for reducing film deposition on the processing equipment. Additionally, the present invention relates to a semiconductor processing system employing a protective shield and utilizing exhaust control.
Chemical vapor deposition (CVD) systems are used to form a thin, uniform layer or film on a substrate such as a semiconductor silicon. During CVD processing, the substrate is exposed to one or more gaseous substances such as silane, phosphane, diborane, oxygen, ozone and the like, and chemical vapors such as TEOS (tetraethylorthosilicate), TMB (trimethylborate), TMPi (trimethylphosphite), TEB (trimethylborate), TEPo (triethylphospate) and the like. The gases are injected into a clean, isolated reaction chamber and allowed to mix and interact with the other gases and/or the surface of the substrate to produce the desired film. The CVD systems typically employ injectors which deliver the gaseous substances directly to the surface of the substrate. An exhaust system removes waste products, such as unreacted gases and powders formed during the reaction, from the reaction chamber. Over time, films are deposited on the exposed surfaces of the chamber creating sources of particulate contamination which may become embedded in the film or degrade film uniformity. In many applications including semiconductor processing, film characteristics such as purity and thickness uniformity must meet high quality standards. To preserve film quality and prevent unacceptable defect levels, the reaction chamber must be cleaned to remove the deposited films.
The injection ports are typically positioned less than one inch from the surface of the substrate. With this limited clearance between the injector and the substrate surface, the surfaces of the injector and chamber walls will become coated with the material produced during the reactions. To reduce the amount of build-up in this area, some CVD systems include shields which are positioned in front of the injectors and exhaust port. The shields include a perforated screen welded to a support body. Supply tubes deliver an inert gas such as nitrogen to the volume between the support body and the screen. The nitrogen exits the shield through the perforated screen to slow the rate at which materials accumulate on the shield during processing.
The desired reactions for chemical vapor deposition typically occur at elevated temperatures, for example 300xc2x0 C. to 600xc2x0 C., with the substrate and chamber being heated to the appropriate temperature for a selected process. The high temperatures in the reaction chamber create thermal stresses in the perforated screen which may cause the screen to buckle after a period of time. The thermal deformation of the perforated screen disrupts the uniform flow of nitrogen through the screen, leaving portions of the screen unprotected against the accumulation of deposition materials. The ability of the screen to deliver nitrogen to the reaction chamber is further reduced as the screen becomes coated with deposition materials, requiring removal and cleaning or replacement of the shield. Since the screen essentially defines an upper xe2x80x9cwallxe2x80x9d of the reaction chamber, the deformed screen also interferes with the uniformity and distribution of the process reactant chemistries within the reaction chamber. The delays created by removal of the shield for cleaning or the replacement of a damaged shield are time consuming and expensive. A shield in which thermal deformation of the screen is minimized or eliminated is desirable. A shield which provides a uniform supply of the inert gas to the reaction chamber is also desirable. A shield in which a damaged screen surface can be quickly and inexpensively replaced is similarly desirable.
For atmospheric pressure CVD (APCVD) processing, the substrates are transported during processing by a conveyor which carries the substrates through one or more reaction chambers. The reaction chamber is not an enclosed chamber, but is merely the area in front of the injector between a series of curtains which use an inert gas such as nitrogen to isolate the reaction chamber from the rest of the process path. The exhaust vents on either side of the injector are used to extract unused gases and reaction by-products from the reaction chamber. If the exhaust is extracted at a rate slower than the rate at which the gases are introduced to the reaction chamber, some of the reactants may escape from the reaction chamber. Thus, with prior art systems the flow rate of the exhaust is typically greater than the rate at which gases are injected into the chamber, with excess inert gas being drawn into the reaction chamber from the area between the reaction chambers to provide a buffer zone blocking the escape of reactant gases. However, the gas drawn into the chamber from the adjacent buffer zones is not uniformly metered across the width of the reaction chamber. Thus, a non-uniform gas-to-gas boundary is created along the width of the reaction chamber. A shield which effectively prevented the escape of reactant gases from the reaction chamber without interfering with the reaction chemistries is desirable. As gases are pulled into the exhaust vent from the area below the injector on one side of the vent and the buffer zone between the reaction chambers on the other side of the vent, a large volume of reactant gas recirculation is created between the opposing flow streams. A shield which efficiently exhausts reactant gases from the chamber and minimizes the amount of gas recirculation within the reaction chamber is desirable.
It is a primary object of the present invention to provide a shield assembly for protecting the exposed surfaces of a gas injector, chamber wall, or exhaust vent used in CVD processing.
It is a further object of the present invention to provide a shield assembly which uniformly delivers an inert gas to surfaces of the shield assembly during extended use of the shield assembly, and allows use of a smooth undistorted surface shape.
It is another object of the present invention to provide a shield assembly which will withstand the high temperatures necessary for the chemical reactions occurring within the chamber, without gas leakage or deformation of the shield assembly or surface delivering protective gas flow.
It is yet another object of the present invention to provide a shield assembly with removable and replaceable screens.
It is another object of the present invention to provide a shield assembly which provides separate dual exhaust paths for reactant gases and by-products versus ambient gas drawn into the chamber.
It is still another object of the present invention to provide a shield assembly which creates an inert gas buffer zone preventing the escape of reactant gases from the chamber.
It is another object of the present invention to provide a shield assembly which can supply excess inert gas to flow out of the chamber instead of requiring adjacent ambient gas to be drawn into the chamber in order to prevent the escape of reactant gases from the chamber in an open APCVD system.
It is an additional object of the present invention to provide a shield assembly which minimizes recirculation of the reactant gases within the chamber while protecting the exhaust vent path surfaces.
Another object of the present invention is to provide a shield assembly allowing a new muffle design having APCVD process modules or chambers isolated by buffer modules which extract excess inert gas from the chambers rather than supply excess gas drawn into the process chambers.
A more general object of the present invention is to provide a shield assembly which has a prolonged useful life, reducing the maintenance costs and maximizing the operational time of the CVD system, and which may be economically and efficiently manufactured and maintained.
It is a further object of the present invention to provide a shield assembly that is constructed of a base having a continuous unit frame for easy, yet secure, insertion of a sheet or screen.
In summary, this invention provides a durable protective shield for protecting the CVD equipment from excess film deposition and safely isolating the reaction chamber from the remainder of the process path. The shield includes a frame assembly including a pair of spaced end walls and a pair of side walls extending between and mounted to the end walls. A plurality of shield bodies are carried by the frame assembly, including injector shield bodies positioned for protection against injected reagents from the injector and shunt shield bodies spaced from the injector shield bodies for protection against exhausted reagents. Each of the shield bodies include a base, a perforated sheet carried by the base, a plenum between the base and the perforated sheet, and a gas delivery device for delivering an inert gas to the plenum at a flow rate such that the gas diffuses through the perforated sheet. In one aspect of the invention, the shield bodies are captured within the frame assembly such that the shield bodies can freely expand and contract relative to the frame assembly under varying temperature conditions. In another aspect of the invention, the perforated sheets are captured by the shield body base and end walls such that the sheets can freely expand and contract relative to the base and end walls under varying temperature conditions, maintaining the precise geometry requirements for CVD films. In another aspect of the invention, the shunt shield bodies each include an outlet port for supplying inert gas to areas below the shield to form buffer zones of inert gas on either side of the deposition zone within the processing chamber.
The invention also includes an atmospheric pressure chemical vapor deposition system which includes a plurality of processing chambers each having an injector therein for injecting reagents into the processing chamber and exhaust vents positioned on opposite sides of the injector. A conveyor transports substrates through the processing chambers along a process path. A plurality of buffer chambers isolate the processing chambers from the rest of the process path. A muffle encloses the processing chambers, the buffer chambers and the process path of the conveyor, and includes by-pass ducts for venting the buffer chambers of muffle. A protective shield is mounted in the processing chambers for protecting the surface of the injector and the inlets of the exhaust ports. The protective shield includes injector shield bodies positioned adjacent the injector and shunt shield bodies spaced from the injector shield bodies. The shield includes an inlet port between the injector shield bodies and an outlet port between the shunt shield bodies for the flow of reagents through the protective shield. The shunt shield bodies each include a plenum filled with an inert gas and a bottom outlet port coupled to the plenum for delivering a supply of inert gas below the protective shield to form buffer barriers on opposite sides of the injection ports. This APCVD system configuration is novel in that the new protective shield can supply excess inert gas from within the processing chambers such that all flow within the buffer chambers exits the muffle through by-pass ducts instead of being drawn into the chamber process exhaust vents.
In a new embodiment of the present invention, a protective shield for gas distribution systems is provided that includes a frame assembly including a pair of spaced end walls and a pair of side walls extending between and mounted to the end walls. A plurality of unit shield bodies carried by said frame assembly are provided. Each of the unit shield bodies is formed of a single piece base and the base has a unit frame formed around the perimeter of the base, a perforated sheet carried by said unit frame, a plenum partially defined by the base and the perforated sheet, and a gas delivery device for delivering an inert gas to the plenum at a flow rate such that the gas diffuses through the perforated sheet.
Additional objects and features of the invention will be more readily apparent from the following detailed description and appended claims when taken in conjunction with the drawings.